The present invention relates generally to clipping circuits and more particularly to clipping circuits which can be adjusted between a maximum level determined by a passive clipping element and a minimum which approaches zero.
Clipping circuits have long been used in the electronics industry for preventing a signal level from exceeding a given upper level. Some such known circuits clip signals of a single polarity, i.e., either positive or negative, while other circuits are known for clipping signals having levels above a given level for both polarities. In addition, other clipping circuits have been developed which are not necessarily symmetric about zero volts, i.e., the clipping level might be, for example, above plus 6 volts and below plus 1 volt.
The limitation of these prior art clipping circuits, however, is that the clipping level is generally a function of the passive clipping element in the circuit itself (such as a zener diode) which does not have an adjustable clipping level. In addition, with respect to passive clipping elements such as zener diodes, the minimum clipping level is typically in the order of 1.8 volts. In order to obtain a lower clipping voltage such as around 0.5 volts, one can utilize the forward breakdown characteristics of a device such as single junction reference diode such as those manufactured by the Codi Corp. In either case, however, the clipping voltage cannot be adjusted lower than that for the passive clipping element thereby making it impossible to produce a simple clipping circuit having a clipping level compatible with high gain low signal level operational amplifiers and the like. In addition, without elaborate electronics, clipping circuits have not heretofore been easily designed having a desired clipping level especially when the desired clipping level is below approximately one-half volt.
In view of the foregoing difficulties with known clipping circuits, it is the principal objective of the present invention to provide a clipping circuit permitting adjustment of a clipping level between a maximum determined by a passive clipping element and a minimum which approaches zero.
It is a further objective of the invention to provide a clipping circuit with an adjustable clipping level which may be adjusted to almost zero volts wherein the circuit may provide symmetrical clipping.
It is still a further objective of the invention to provide an adjustable clipping circuit wherein the clipping levels and their symmetry are both adjustable.